The intercom is a remote control for operational communication. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Telephony

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This simple intercom will help you quickly establish communication, it will be useful for telephoning various premises, production areas. The communication range of the intercom depends on the resistance of the line and can reach three kilometers.

Its schematic diagram is shown in the figure. Subscribers (there may be 10 in total) have telephone sets indicated on the diagram TA1-TA10. All other elements are combined into an attendant console (the figure shows how the console looks like for three subscribers). On the top panel of the console are: a switch and a power supply signal lamp (SA12 and HL12); switches and signal lamps for calling subscribers (SA1-SA10 and HL1-HL10); call button (SB1); line health monitoring LED (HL 11); horn switch (SA11); handset connector (XS1).

Let's see how the device works in different modes. Suppose the attendant needs to talk to the subscriber who has the TA1 device installed. To do this, he switches the SB1 button to the "call" position. In this case, alternating current is supplied to the device TA1 through the circuit: the upper terminal of the winding II of the transformer T1, the diodes VD1-VD4 and the LED HL11, the closed contacts (lower according to the scheme) of the SB1 button, the lower contacts of the switch SA1, the apparatus TA1, the lower terminal of the winding II of the transformer, In the telephone set, the bell rings and the HL11 LED lights up, indicating that the line is working. The subscriber, having heard the call, picks up the phone and can carry on a conversation with the telephone operator on duty. In this case, the current will flow through the circuit: the power source, the TA1 device (its handset), the lower contacts of the switch SA1, the normally closed contacts of the SB1 button, the BM1 microphone and the telephone BF1 of the attendant's handset, the resistor R22, the common wire of the power source. If another subscriber needs to be connected to the conversation, he is called in the same way. Any number of subscribers can participate in a conversation. True, this will reduce the volume a little.

And if the subscriber wishes to call the telephone operator on duty? Then it is enough for him to pick up the receiver of his telephone. A positive voltage will be applied to the base of the transistor VT1 through the resistance of the tube of the device, the normally closed contacts of the switch SA1 and the resistor R1. Transistor VT1 will open and the signal lamp of the first subscriber HL1 will light up. The current flowing through this lamp will create a voltage drop across the resistor R12, and the transistor VT11 will open. The output 13 of the logic element DD2.4 will receive a signal 1, allowing the operation of the sound signal. The attendant will hear a tone call, see the burning lamp HL1, move the SA1 switch to another position and be able to carry on a conversation. And the long beeps that sounded in the subscriber's handset indicate that the line is working, that the person on duty at the central console is not talking to anyone.

And now let's talk about the work of the node of the sound signal and beeps. On the elements DD2.1-DD2.3 of the DD2 microcircuit, a generator is assembled that generates a signal with a frequency of about 400 Hz, and on the elements DD1.1-DD1.3 and transistors VT12, VT13 - a pulse generator with a frequency of 0,3 ... 2 Hz . If the transistor VT12 is closed, the generator generates long beeps (0,3 Hz); if this transistor is open, short beeps (2 Hz) are formed. At the logic element DD1.4, the signals of the two generators are summed up and fed into the lines of telephone sets (through the divider R18, R19), as well as through the logic element DD2.4 to the transistor VT14, which is loaded on the dynamic head BA1.

If during a conversation one of the subscribers picks up the phone, he will hear short beeps, since the VT12 transistor will be opened by the voltage drop created by the conversational current across the resistor R22 (about 3 V). The operator on duty will also hear short beeps generated by the dynamic head BA1, in addition, a signal lamp will light up on the remote control. He will connect the subscriber to the conversation or ask him to hang up and wait, and then call as soon as the line is free. If necessary, the duty officer can turn off the sound signal with the SA11 switch.

The intercom is powered by the mains. Transformer T1 lowers the mains voltage to 36 V (the window is used when calling) and to a voltage of 22 V. This voltage is rectified by the diode bridge VD8--VD11, the ripples are smoothed out by capacitor C5, then the voltage is stabilized by a stabilizer on the VT15 transistor connected according to the emitter follower circuit, and on zener diodes VD6, VD7. The output is a constant voltage of 20V. For HL1-HL10 lamps, it is not necessary to stabilize the voltage, so they are powered directly from the VD8-VD11 rectifier. This inclusion made it possible to reduce the heating of the VT15 transistor. Chips DD1.2 are powered by the simplest parametric stabilizer VD5R24.

Details and design. The device uses widely used parts. As chips DD1, DD2, in addition to K155LAZ, you can also use chips of types K158LAZ, K555LAZ. Transistors VT1-VT10 can be any of the KT815B, KT603, KT608, KT3117 series; VT12, VT13 - any of the KT201, KT312, KT315, KT316, KT603, KT608 series; VT14 - KT315, KT603, KT608, KT815 with any letter; VT15 - any of the KT801 series. KT815, KT817, VT11 - KT203, KT208, KT361 with any letter. LED HL11 - any of the series AL102, AL112, AL307, AL310., All capacitors, except for C2, type K50-6 or K50-16, C2 - KM-6, K10-7v, K10-17. All resistors type MLT. Switches SA1-SA10, switches SA11, SA12 type "tumbler" (MTD-1,TP1-2,P1T, MT1); button SB1 type KM-1, KMD-1, KP-3, P2K, and socket XS1 - SG-5, plug XP1 - SSh5. Fuse FV1 - 0,15-0,5 A (depending on the number of subscribers). As a power transformer, it is convenient to use the vertical scan output transformer of the TVK-110LM TV. Windings, except for the primary, are removed and two new windings are wound. Winding II should contain 410 turns of PEV-2 wire 0,12 mm, winding III - 250 turns PEV-2 0,25 mm. When disassembling the transformer, care must be taken, otherwise the leads of the primary winding can be cut off. The VT15 transistor is mounted on a 40x20 mm duralumin plate - it serves as a radiator. As a dynamic head BA1 or BF1, a TA-4 capsule with a resistance of 65 ohms was used. Carbon microphone BM1 - any type, for example MK-16-U.

Telephone sets can be, for example, TAI-66, TAN-70. If you are using a device with a faulty dialer, disconnect the conductors from it and connect them to the lever switch so that when the handset is down, a call is connected to the line through a 1 uF capacitor, and when the handset is up, a microphone and telephone are connected in series.

When checking and adjusting the intercom, by selecting the resistor R23, the desired tone of the audio signal is set. Select resistor R22 so that when a conversational current flows through it and the device, the voltage drop is at least 3 V.

Any wire can be used to connect telephones to the attendant's console.

Author: A. Evseev; Publication: cxem.net

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